Do underdrive pulley really work
Define "work" they certainly do slow the accessories down the advertized amount.
That said since the waterpump on the LT1 is not belt driven we have a lot less accessory load to start with.
With a stock cam/idle they can cause charging issues, the raised idle of a cammed setup will usually offset this,
Bottom line is most of us find pulling the belt to be worth something like .1 at that it stands to reason that a 34% underdrive pulley could only gain at most .034. Those who have bought them will have things to say like "it revs faster" and other deeply scientific analysis like that. Look at my logic though.
I would not buy an underdrive piggyback pulley.
Now if I needed to buy a damper I would certainly buy an aftermarket underdrive one long as I had to buy a replacement, but for now I am using a stocker.
That said since the waterpump on the LT1 is not belt driven we have a lot less accessory load to start with.
With a stock cam/idle they can cause charging issues, the raised idle of a cammed setup will usually offset this,
Bottom line is most of us find pulling the belt to be worth something like .1 at that it stands to reason that a 34% underdrive pulley could only gain at most .034. Those who have bought them will have things to say like "it revs faster" and other deeply scientific analysis like that. Look at my logic though.
I would not buy an underdrive piggyback pulley.
Now if I needed to buy a damper I would certainly buy an aftermarket underdrive one long as I had to buy a replacement, but for now I am using a stocker.
Staging Lane
Joined: Dec 2005
Posts: 87
Likes: 1
From: Bucks County
I bought a used set of march underdrive pulleys (crank + alt) and really can't say I notice a difference. I don't experience any charging issues but do notice the power steering is not as strong when in parking lots. For $30 bucks used I couldn't pass it up, I would estimate a 2 hp gain and thats on the high end.
On The Tree
Joined: Jan 2008
Posts: 130
Likes: 0
I had one and got rid of it. It does what it says, but mine was made so that you slip the pully over the stock harmonic balancer. This adds a good chunk of rotational mass and IMO defeats the gain from the pullies being under driven.
TECH Regular
Joined: Apr 2011
Posts: 441
Likes: 0
From: Deep in the heart of Texas
I had one, I changed back to stock after experiencing charging issues and an alternator charge. I don't think it was the direct reason for the fried alternator but the horsepower loss was not noticed after the stock pulley was in place.
Last edited by 93 LT1 Vette; Apr 4, 2012 at 08:48 PM.
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